A method consisting of oxidising cyclohexanone is typically known as a method of producing .epsilon.-caprolactone.
The method of oxidising the cyclohexanone is a method of cooxidation using aldehyde(s) or a method using organic peroxides as oxidising agent.
Peracetic acid, perpropionic acid, perisobutyric acid or the like are used as the organic peracids.
Acetaldehyde, benzaidehyde, alkyl-substituted benzaldehydes or the like are used as aldehydes for the co-oxidation.
The synthesised carboxylic acids may, for example, in case of aliphatic carboxylic acids be directly used as products for industrial use; in case of aromatic carboxylic acids, they can be transformed through a further oxidation into adipic acids or the like.
.epsilon.-caprolactone is polymerised and then used as a moulding material, for polyester polyols, for biodegradable plastics or the like. However, during polymer production, there is an influence on the polymerisation reaction, and there are risks of obtaining discoloured resins. This is due to the great influence of the impurities contained in the .epsilon.-caprolactone on the reaction rate and on the colour hue of the polymer. Particularly, the content of the small amount of impurities contained in the .epsilon.-caprolactone, the acid value thereof, the water content thereof or the like should be optionally reduced, since they have an influence on the polymerisation reaction-rate, on the value obtained at the thermal discoloration stability test (APHA) of the .epsilon.-caprolactone itself and on the colour hue (APHA) of the resins obtained after polymerisation.
Consequently, the purpose of the present invention is to provide an .epsilon.-caprolactone which presents few discoloration risks during monomer formation/storage and during polymer formation as well as use thereof and to provide a method of producing such an .epsilon.-caprolactone. The purpose of the invention is also to provide polycaprolactone(s) having low discolorability by using the .epsilon.-caprolactone and to provide a method of producing these polycaprolactones.